Because the multimedia époque has created a demand for increased volume and speed of information processing in optical communication systems and computers, transmission systems using light as a transmission medium have been finding application in public communication networks, LAN (local area networks), FA (factory automation), interconnectors between computers, household internal wiring, and the like. Among the elements constituting the transmission systems, optical waveguides are the basic structural elements, for example, in optical devices for realizing high-volume information transmission of movies and dynamic images, optical computers, optoelectronic integrated circuits (OEIC), and optical integrated circuits (optical IC). Optical waveguides have been actively studied because of a large demand for them. Especially, high-performance and low-cost products are especially required.
Quartz optical waveguides and polymer optical waveguides are known as optical waveguides.
Among them, quartz optical waveguides have an advantage of a low transmission loss. However, quartz optical waveguides have disadvantages of causing process-related problems which include a high temperature required in the processing of the manufacturing step, and difficulties encountered in the production of optical waveguides having large surface areas.
Further, the advantages of polymer optical waveguides include easiness of processing and a large degree of freedom in material design. For this reason, the use of polymer materials such as poly(methyl methacrylate), polycarbonate and the like have been studied. However, polymer optical waveguides usually have poor heat resistance. For this reason, fluorinated polyimides that have excellent heat resistance and transmission loss have been widely researched in recent years.
However, when polymer materials are used, it takes a lot of time to produce polymer optical waveguides, because dry etching is required for forming core portions of polymer optical waveguides as required similarly in the production of quarts optical waveguides.
Under these circumstances, photocurable materials such as epoxy UV-curable resins having photolithographic capability, and optical waveguides using such photocurable materials have been recently suggested (for example, see claim 1 of Japanese Patent Application Laid-open (JP-A) No. H6-273631).
As described above, the problems associated with the conventional polymer optical waveguides are that the waveguide loss in the region of a wavelength of 650-1600 nm is comparatively high, heat resistance is poor, and some of the characteristics required for the optical waveguides are unsatisfactory.
In order to resolve these problems, chemical treatment methods of the polymer such as fluorination or deuteration substitution have been studied. When such chemical treatment methods are used, adhesion to the substrate degrades, and long-term reliability deteriorates. Also, when the chemically treated polymer is used for the core portion, the refractive index may not be increased to the desired level.